JP2013140716A - Shield flat cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shield flat cable for use in the LVDS system, in which the far-end crosstalk is -24 dB or less within a frequency range up to 6 GHz for a distance exceeding 0.4 m.SOLUTION: In the shield flat cable, four or more flat type conductors are arranged on one plane, and insulated by bonding an insulation film from the top and bottom of an array surface, an intervening layer is provided on the outside of the insulation film, and a shield layer is provided on the outside of the intervening layer. The differential mode impedance is adjusted in the range of 75-110 Ω excepting the terminal processing part, and following relations are satisfied εa<εb and 0.86≤εe/ε1, where ε1 is the effective dielectric constant of the insulation film, εa is the dielectric constant of an adhesive layer, εb is the dielectric constant of a base material layer, when the insulation film consists of two layers, i.e., an adhesive layer adhering to the conductor and a base material, and εe is the effective dielectric constant of a nonmetal layer from the flat type conductor to a shield layer.

Description

  The present invention relates to a shielded flat cable in which a plurality of rectangular conductors are arranged in parallel, an insulating resin film is bonded together, and a shield film is bonded to the outside.

  Patent Document 1 discloses a shielded flat cable used for low voltage differential transmission (LVDS). In this shielded flat cable, an insulating resin film to be bonded to a flat conductor is made of an adhesive layer and an insulating layer. It is disclosed that polyester resin, polyphenylene sulfide resin, polyimide resin or the like is used for the insulating layer, and that a flame retardant added to the polyester resin or polyolefin resin is used for the adhesive layer. .

JP 2009-146694 A

The far end crosstalk cannot be ignored as the cable length increases and the transmitted signal has a higher bit rate. There is no practical means to compensate for noise due to inter-channel crosstalk chains, and the increase in crosstalk can be a serious problem.
On the other hand, with the increase in size of devices including flat panel displays, longer cables have been required. As the image quality becomes higher, the transmission capacity becomes larger and higher speed transmission is required.
The present invention is a shielded flat cable used for high-speed signal transmission wiring of a differential transmission system typified by the LVDS system, and has a far-end crosstalk of −24 dB in a frequency range up to 6 GHz at a distance exceeding 0.4 m. It aims at providing the shield flat cable used as the following.

  In the shielded flat cable of the present invention, four or more rectangular conductors are arranged on one plane, an insulating film is bonded from above and below the arrangement surface to insulate the rectangular conductor, and an intervening layer is provided outside the insulating film. A shielded flat cable having a shield layer outside the intervening layer, wherein the differential mode impedance of the portion excluding the terminal processing portion is adjusted to a range of 75 to 110Ω, and the effective relative dielectric constant of the insulating film is ε1 The insulating film is composed of two layers, an adhesive layer that adheres to a conductor and a base material layer, where the relative dielectric constant of the adhesive layer is εa, the relative dielectric constant of the base material layer is εb, and shielding from the rectangular conductor Εa <εb and 0.86 ≦ εe / ε1 when the effective relative dielectric constant of the non-metal layer up to the layer is εe.

  The flat cable of the present invention has a far-end crosstalk of −24 dB or less in the frequency range up to 6 GHz at a distance of 450 mm due to the above configuration.

It is a perspective view which shows the flat cable of this invention. It is sectional drawing perpendicular | vertical to the length direction of the flat cable of this invention. It is sectional drawing perpendicular | vertical to the length direction of the flat cable of this invention of another aspect. It is sectional drawing perpendicular | vertical to the length direction of the flat cable of this invention of another aspect. It is sectional drawing perpendicular | vertical to the length direction of the principal part of the flat cable of this invention. It is sectional drawing perpendicular | vertical to the length direction of the principal part of the flat cable of this invention. It is a table | surface which shows the Example and comparative example of this invention. It is a table | surface which shows the Example and comparative example of this invention.

As shown in FIG. 1, the shielded flat cable 1 of the present invention has a plurality of flat conductors 2 arranged in parallel on one plane, and an insulating film 3 is bonded from above and below the parallel surface to insulate each conductor 2. Since the flat cable of the present invention is used for differential transmission of two or more channels, four or more signal lines are required. That is, four or more flat conductors are necessary. In the figure, four rectangular conductors 2 are used, but any number may be used as long as there are four or more. Some flat rectangular conductors may be used for ground lines in addition to signal lines.
In the shielded flat cable 1 of the present invention, an intervening layer 7 for adjusting the dielectric constant is attached to the upper and lower insulating films 3. The intervening layer 7 comprises an adhesive layer 8 for adhering to the insulating film and a base material layer 9 acting for adjusting the refractive index. The base material layer 9 is a dielectric layer made of resin or the like, and preferably has a low dielectric constant.

The shield flat cable 1 of the present invention is one in which a shield film 4 is wound or affixed outside an intervening layer 7 to form a shield layer. The shield film 4 may be wound so as to wrap around the intervening layer 7 as shown in FIG. As shown in FIG. 3, the shield film 4 may be attached to the intervening layer 7. In this case, there are two shield films 4, and the shield films 4 are not integrated. As shown in FIG. 4, it may be affixed only on one side (the lower side in FIG. 4) of the flat cable. In this case, the intervening layer 7 is also only on the one surface, and the shield film 4 is pasted outside (lower side in FIG. 4). Only one side of the shielded flat cable 1 is shielded.
As the shield film 4, those conventionally used, for example, one in which an adhesive layer is formed on one surface of a copper foil or an aluminum foil and a resin film or the like is pasted on the other surface can be used.

  The thickness or width of the flat conductor 2, the interval between the flat conductors 2, the dielectric constant of the insulating film 3 and the intervening layer 7 are adjusted so that the characteristic impedance of the flat cable is any value between 75Ω and 110Ω.

The insulating film 3 of the present invention includes an adhesive layer 5 and a base material layer 6. Although only one layer of the adhesive layer 5 and the base material layer 6 is shown in FIGS. 1 to 4, each may be formed of a plurality of layers.
The adhesive layer 5 is a thermoplastic resin, and is made of a material that can be bonded to the flat conductor 2 or the counterpart insulating film 3 by applying heat of several hundreds of degrees Celsius. For example, a polyester-based adhesive can be used for the adhesive layer 5.
Even when heat of a few tens of degrees Celsius is applied to bond the insulating film 3, the base material layer 6 maintains the shape of the film without softening or showing adhesiveness. Polyester such as polyethylene terephthalate can be used for the base material layer 6.
Since the adhesive layer 5 and the base material layer 6 have different functions, they are different resins.

The intervening layer 7 of the present invention comprises an adhesive layer 8 and a base material layer 9. Although only one layer of the adhesive layer 8 and the base material layer 9 is shown in FIGS. 1 to 4, each may be formed of a plurality of layers.
The adhesive layer 8 is a thermoplastic resin and is made of a material that can adhere the insulating film 3 and the base material layer 9 by applying heat of several hundreds of degrees Celsius. For example, a polyester-based adhesive can be used for the adhesive layer 8. The adhesive layer 8 may be made of a material different from that of the adhesive layer 5.
The base material layer 9 is a dielectric having a low dielectric constant for adjusting impedance. Polyester film such as polyolefin resin film or polyethylene terephthalate can be used for the base material layer 9. A foamed resin film can also be used.

In a differential transmission path through which an electric signal propagates, it can be understood that electric lines of force are emitted from a conductor having a positive potential to a conductor having a negative potential. As for the electric potential of the conductor, + − alternates with time, and FIG. 5 shows a state at a certain moment. However, the electric lines of force are only shown for explanation.
Two flat conductors 12 form a pair. The rectangular conductor 12a has a positive potential at this moment, and 12b has a negative potential. The electric lines of force 10a from the flat conductor 12a having a positive potential enter the adjacent flat conductor 12b having a negative potential and the ground line 11 adjacent to the flat conductor 12a. The electric field lines 10c from the adjacent ground line 13 also enter the flat conductor 12b. The electric lines of force 10b going out of the cable pass through the insulating film 3 and the intervening layer 7 in order, but are refracted at the interface because the refractive indexes of the two layers are different.

  The refraction of the electric lines of force 10b can be explained by Snell's law. The refractive index can be replaced by the square root of the product of dielectric constant and permeability. Here, since both the insulating film 3 and the intervening layer 7 are plastic materials and their magnetic permeability can be assumed to be equal, the refractive index is determined by the ratio of the square root of the dielectric constant. Assuming that the incident angle of the lines of electric force 10b from the insulating film 3 to the intervening layer 7 is θ1, the refraction angle is θ2, the relative dielectric constant of the insulating film 3 is ε1, and the relative dielectric constant of the intervening layer 7 is ε2, ε1 × sin θ1 = ε2. Xsin θ2. The relative dielectric constant is a value when the vacuum dielectric constant is 1. In the case of ε1> ε2, the electric lines of force are refracted so that θ1 <θ2 as shown by electric lines of force 10b2 in FIG. In the case of ε1 <ε2, the light is refracted so that θ1> θ2 as shown by the electric force line 10b1.

  The insulating film 3 is refracted at the interface between the adhesive layer 5 and the base material layer 6, and the intermediate layer 7 is refracted at the interface between the adhesive layer 8 and the base material layer 9. As shown in FIG. 6, the incident angle of the electric force lines 10b from the adhesive layer 5 to the base material layer 6 is θa, the refraction angle is θb, the relative dielectric constant of the adhesive layer 5 is εa, and the relative dielectric constant of the base material layer 6 If the rate is εb, then εa × sin θa = εb × sin θb. In the case of εa> εb, the electric lines of force are refracted so that θa <θb as shown by electric lines of force 10b2 in FIG. In the case of εa <εb, the light is refracted so that θa> θb as shown by the electric lines of force 10b1.

When the effective relative dielectric constant of the insulating film including the insulating film and the intervening layer is ε, ε is a weighted average of ε1 and ε2. In the cross section of FIG. 2 etc., if the cross sectional area of the insulating film is S1, and the cross sectional area of the intervening layer is S2, ε = (ε1S1 + ε2S2) / (S1 + S2)
In the case of FIG. 5, the effective relative dielectric constant of the nonmetallic layer from the flat conductor to the shield layer is the combined dielectric constant of the insulating film 3 and the intervening layer 7. By making the relative dielectric constant of the insulating film 3 smaller than the relative dielectric constant of the intervening layer 7, the combined relative dielectric constant (in other words, the effective relative dielectric constant of the nonmetallic layer from the flat conductor to the shield layer) is insulated. The relative dielectric constant of the film 3 becomes larger.

In the shielded flat cable of the present invention, the dielectric constants of the adhesive layer 5 and the base material layer 6 in the insulating film 3 are different, and the dielectric constants of the insulating film 3 and the intervening layer 7 are also different. In the present invention, the dielectric constant (εa) of the adhesive layer 5 is made smaller than the dielectric constant (εb) of the base material layer 6. And the ratio with respect to the dielectric constant of the insulating film 3 of the effective dielectric constant of the nonmetallic layer from a flat conductor to a shield layer shall be more than a fixed value. Specifically, the ratio of the effective relative dielectric constant to the relative dielectric constant of the insulating film 3 is set to 0.86 or more. As a result, the electric field lines coming out of the flat conductor 2 can be confined in the vicinity of the flat conductor 2, and even when high-frequency transmission is performed in which the occupied frequency bandwidth of a signal per channel reaches 6 GHz at a distance of 450 mm. Crosstalk can be reduced.
The relative dielectric constant of the intervening layer 7 may be larger than the relative dielectric constant of the insulating film 3. However, if the relative dielectric constant of the intervening layer becomes too large, the intervening layer becomes thick for impedance adjustment. In order to make the thickness of the shield flat cable suitable for practical use, there is an upper limit in the value of the relative dielectric constant of the intervening layer. In this respect, it is preferable that the ratio of the effective relative dielectric constant of the nonmetallic layer from the flat conductor to the shield layer to the relative dielectric constant of the insulating film 3 is 1.1 or less.

(Example)
In Examples 1 to 4 and Comparative Examples 1 to 3, as shown in FIG. 3, the dielectric layer (intervening layer) 7 for impedance adjustment and the outside (on the opposite side to the flat conductor 2) are provided on both of the insulating films 3. A shielded flat cable 1 having a shield film 4 attached thereto was manufactured. The intervening layer 7 is formed by attaching the adhesive layer 8 to one surface of the base material layer 9, and the adhesive layer 8 is attached to the insulating film 3.
In this embodiment, since there are two adhesive layers, the adhesive layer 5 of the insulating film 3 is called the insulating adhesive layer 5, and the adhesive layer 8 that bonds the intervening layer 9 to the insulating film 3 is called the intervening adhesive layer 8. As for the base material layer, the base material layer 6 of the insulating film is called the insulating base material layer 6, and the base material layer 9 of the intervening layer is called the intervening base material layer 9.
In any example, the ground line is represented by G, the signal line is represented by S, and the arrangement thereof is arranged as GSSGSSG. Two adjacent signal lines are paired to form one channel. There is a ground line between each channel.

The magnitude relationship between the relative dielectric constant εa of the insulating adhesive layer 5 and the relative dielectric constant εb of the intervening base material layer 6 was as shown in FIG. The relative dielectric constant ε1 of the insulating film 3, the relative dielectric constant εe of the insulating film 3 and the intervening layer 7 and their ratio are also shown in FIG.
FIG. 7 also shows the far-end crosstalk (maximum value) and differential mode impedance between adjacent channels of these shielded flat cables. The far-end crosstalk maximum value at 6 GHz is −24 dB or less (6.25% crosstalk amount compared to the main signal), and the one below −26 dB (5% crosstalk amount compared to the main signal) is excellent. did.

The dielectric constant of each layer was measured using an impedance material analyzer as a thickness of 0.5 mm or more by stacking the layers. The relative dielectric constant is a ratio to the dielectric constant of vacuum.
When the relative dielectric constant of the insulating adhesive layer is εa, the relative dielectric constant of the base material layer is εb, and the relative dielectric constant of the insulating film composed of the insulating adhesive layer and the base material layer is ε1, if ε1 <εb, then εa < εb.

As shown in Examples 1 to 4, the relative dielectric constant εa of the insulating adhesive layer <the relative dielectric constant εb of the base material layer, and the insulation with the effective relative dielectric constant εe of the nonmetallic layer from the flat conductor to the shield layer If the ratio of the relative dielectric constant ε1 of the film is εe / ε1 ≧ 0.86, the far-end crosstalk is acceptable at a distance of 450 mm and 6 GHz. In these embodiments, it is considered that the far-end crosstalk is small because the electric field lines coming out of the flat conductor 2 are confined in the vicinity of the flat conductor 2.
Comparative Example 1 is a shielded flat cable having a conventional configuration. In this example, far-end crosstalk at a distance of 450 mm at 6 GHz is unacceptable. In this example, the relative permittivity decreases in order from the layer closer to the flat conductor 2 to the layer farther away (the relationship of εa>εb> ε2). The electric field lines coming out of the flat conductor 2 are refracted at the interface of each layer and move away from the flat conductor 2 in the horizontal direction. Further, when electric lines of force are emitted from a layer having a high relative dielectric constant (a layer close to the flat conductor 2) to a layer having a low relative dielectric constant (a layer far from the flat conductor 2), some electric lines of force are totally reflected. To do. These are thought to be the cause of the poor far-end crosstalk.
Comparative Example 2 is an example in which the relative dielectric constant of the intervening layer 7 is larger than that of Comparative Example 1. As a result, εe / ε1 exceeds 0.9, but far-end crosstalk at a distance of 450 mm and 6 GHz is still unacceptable.
Comparative Example 3 is an example in which εa <εb, εe / ε1 is less than 0.86, and the far-end crosstalk of 450 mm and 6 GHz is unacceptable.
Example 2 and Example 4 are examples in which the material of the intervening layer is selected so that the relative dielectric constant of the intervening layer is higher than that of Example 1. In this example, εe / ε1 is 0.93 or more and 1 or less. In these examples, the far-end crosstalk at a distance of 450 mm and 6 GHz is excellent (5% crosstalk relative to the main signal).

Examples 5-6 and Comparative Examples 4-5 are examples in which the intervening layer 7 is only on one side of the insulating film 3 as shown in FIG. 4 and only one side is shielded. The arrangement of the signal line S and the ground line G is the same as in Examples 1-4 and Comparative Examples 1-3.
The magnitude relationship between the relative dielectric constant εa of the insulating adhesive layer 5 and the relative dielectric constant εb of the base material layer 6 in each example is as shown in FIG. The relative dielectric constant ε1 of the insulating film 3, the relative dielectric constant εe of the insulating film 3 and the intervening layer 7 and their ratio are also shown in FIG.
The far-end crosstalk between adjacent channels of these shielded flat cables was measured. The far-end crosstalk (maximum value) and differential mode impedance measured for each example are also shown in FIG. The far-end crosstalk maximum value at 6 GHz is −24 dB or less (6.25% crosstalk amount compared to the main signal), and the one below −26 dB (5% crosstalk amount compared to the main signal) is excellent. did.

In Examples 5 and 6, since εa <εb and εe / ε1 ≧ 0.86, 6 GHz far-end crosstalk is acceptable at a distance of 450 mm. In these embodiments, since εe / ε1 ≧ 0.93, the far-end crosstalk is excellent at a distance of 450 mm. In these embodiments, it is considered that the far-end crosstalk is small because the electric field lines coming out of the flat conductor 2 are confined in the vicinity of the flat conductor 2.
Comparative Example 4 is a shielded flat cable having a conventional configuration. In this example, εa> εb, and εe / ε1 is less than 0.86. The far-end crosstalk at 6 GHz with a distance of 450 mm is unacceptable.
In Comparative Example 5, εa <εb, but εe / ε1 is less than 0.86, and the far-end crosstalk of 450 mm and 6 GHz is unacceptable.

DESCRIPTION OF SYMBOLS 1 Shield flat cable 2 Flat conductor 3 Insulating film 4 Shield film 5 Adhesive layer (insulating adhesive layer)
6 Base material layer (insulating base material layer)
7 Intervening layer 8 Adhesive layer (intervening adhesive layer)
9 Base material layer (intervening base material layer)
10 Electric field lines

Claims (1)

Arrange four or more rectangular conductors on one plane, and insulate the rectangular conductors by attaching insulating films from the upper and lower sides of the arrangement surface, provide an intervening layer outside the insulating film, and shield outside the intervening layer A shielded flat cable with layers,
The differential mode impedance of the portion excluding the terminal processing unit is adjusted to a range of 75 to 110Ω,
The effective relative dielectric constant of the insulating film is ε1,
The insulating film is composed of two layers, an adhesive layer that adheres to a conductor and a base material layer, the dielectric constant of the adhesive layer is εa, the relative dielectric constant of the base material layer is εb,
When the effective relative dielectric constant of the nonmetal layer from the flat conductor to the shield layer is εe,
A flat cable, wherein εa <εb and 0.86 ≦ εe / ε1.

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